Potentiometer as low cost position transducer

[skrab]

Hi Everyone,

I need a low cost method to indicate rotary position of a cable winch drum. The wiring distance will be approximately 150 ft from the operator's station to the equipment. I am thinking about a simple series circuit just using a 24VDC power supply, fixed resistor, and linear pot (using only 2 wires as in rheostat.) The resulting variable current would be fed and scaled into a low cost panel meter (there will be no other loading of the circuit.) Note: This will be used only for "rough" indication of the drum position.

Again, cost and ease of implementation is driving this method of position indication. I am aware of higher precision devices. I just do not think this application warrants the higher costs.

Does anyone have a reason that this will not work?

Any and all comments are appreciated.
Thanks in advance

 

[davidbeach]

The pot needs to work through as many revolutions (or be geared down) as the winch drum. 10 turn pots are available, but can your winch be limited to 10 turns?

 

[Barry1961]

Using potentiometers for position feedback is a common practice.

Another limit besides number of turns is the life expectancy of potentiometer. If this is a high cycle application you may not have a very long life cycle.

The 150 foot should not be a problem with good shielded cable.

Barry1961

 

[IRstuff]

Pots are also very noisy, particularly under vibration

TTFN

 

[nbucska]

you can get pot.meters with guaranted life time.

 

[ScottyUK]

What about a pulse counting method using an inductive sensor? More robust, longer life, no limits on rotational life. You can sense any convenient ferrous object on the winch - a bolt head or a hole in the drum would be obvious candidates.

The aggravation saved when the pot breaks will soon offset the extra £50 you spent on the pulse counter.


----------------------------------

One day my ship will come in.
But with my luck, I'll be at the airport!

 

[BJC]

They make fishing reels with digital readouts. You might want to look some of them over. The electrical winches that are used for lowering downriggers ( also availabe at your local sporting goods store ) I am not sure if you could adopt a reel for use but the circuitry might be adotptable.
The other option is to use a pulse counter. Acton instruments is a good place to start.

http://www.actionio.com/

as is Wilkerson Instrument Co.

http://www.wici.com/

You can use off the shelf instruments to count revolutions and tranmit them to an indicator on your panel. I would go for a magnet bolted to the drum or a photocell looking at a painted spot on the drum.
Lastly, google up counters and hoist position indicators. I used a Red Lion counter once to do exactly what your doing. It would count up and down ( used a contact off the hoist control to know if it was going up or down). The one I used just counted, I think they had one with a math function that would convert the pulse to length.
Get the catalogs and application notes from the above and you can come up with something pretty fast that will work. Like this

http://www.redlion.net/Products/Groups/Counter/Rate/CUB5/Docs/01012.pdf

However it's more likely what you want exist and is in use on the Link Belt crane at the nearest construction site.

 

[itsmoked]

Pulse counter ...MUCH better idea.

No noise, power dissipation, or turn limit problems.

 

[Skogsgurra]

You need to make the pulse counter non-volatile if you want to know where the drum is after power down.

Potentiometer is not a bad solution. If you can solve the mechanical part of it - which you probably have. Noise and vibration is not an issue if you are reading out via a simple analogue meter.

Gunnar Englund

http://www.gke.org

 

[Warpspeed]

A multiturn potentiometer should work fine. The drum will need some sort of very rugged mechanical end stop at both limits of rotation, to prevent mechanical damage to the potentiometer.